The terminal systems of the present invention are particularly appropriate in applications where not only is it important to minimize the weight of tension rods, but also it is important to minimize the weight and size of terminal fittings and related hardware by providing relatively light and geometrically slim terminal systems. An important application is sailing yachts, where rigging connects not only at the deck but aloft at many locations along the mast, either at the mast wall or at spreader tips (from which the rigging continues up at an angle and at smaller size), and where in general each rigging line or stay requires fittings at both ends, and many fittings are aloft. If heavy and bulky fittings are required for each end of each stay, cable or rod, the potential advantages of the composite tension rods are largely defeated. These constraints have discouraged widespread employment of composite tension rods in sailing yachts despite the potential for improvement in gross weight and in weight distribution, and the further advantages of freeness from creep, good resistance to abrasion, and dimensional stability under handling or coiling. Composite tension rods reinforced with carbon fibers or other of the fiber materials mentioned above are believed to have been pultruded as rods of circular cross-section and tried in performance applications as diagonals and verticals in yacht rigging, but so far as known, to date no commercially successful design of terminal system has been provided for such rods, and their use has languished.
Applications such as sailing yachts are to be contrasted with systems such as bridge roadway construction where tensioned bridge stays are continuous across the tops of the bridge tower, and require no anchoring fittings aloft, and are connected by anchoring members located at ground points at or near the roadway, where weight and bulkiness is of little or no concern. A known anchoring system for composite carbon-fiber reinforced bridge stays used in such an application is disclosed in U.S. Pat. No. 5,713,169. It includes an “anchor body” or frustum of potting resin that coaxially receives and is bonded to the bridge stay or composite tension member. The wall thickness of the cone of potting resin varies along the cone length, and is always greater than the composite tension member's radius. The cone wall thickness increases along the cone length in such a way as to preserve the strictly conical shape of the cone of resin, and reaches several times the tension member's radius at the back end of the cone of resin, that is, the end opposite to the point where the free length of the tension member enters the front end of the cone. The conical anchor body is slidably received in a steel casting or “anchor casing.” A “slide film,” in the form of a Teflon foil, or a deposit of a “separation agent”, is included for this purpose. The internal surface of the anchor casing must also be strictly conical in shape for this purpose, and the interface between the anchor body and the anchor casing must be free of any adhesive bond or mechanical keying such as threaded engagement at the interface. The ability of the anchor body to slide relative to the anchor casing is necessary to allow for the proper wedging action of the cone and captured compression.
Systems have been proposed for terminating fiber-reinforced tension members used in sailing yachts, but such systems relate primarily to tension members consisting of a wrapped plurality of rods, rather than to monolithic rod pultrudates as in the present invention, and furthermore are subject to constraints similar to those of the bridge stay terminating systems just discussed. U.S. Patent Application Pub. No. 20030010966 shows one such system that, like the system of U.S. Pat. No. 5,713,169 cited above, relies on slippage (paragraph 0067) and on captured compression within a frustum (paragraphs 0053, 0068). The fittings of such systems must be designed to withstand high hoop loads in the fitting (paragraph 0074). Moreover, to a large extent such systems rely on the bundling together of multiple small relatively flexible composite rods. When such rods enter a bulky fitting, the transition from relatively flexible small composite rods to relatively stiff fitting happens in an abrupt manner. This means when the rigging is slack (low tension) the fitting and rods will bend relative to one another, and wear and fatigue at the entrance to the terminal fitting will result in premature failure. (This also happens in conventional wire rigging between the cable and a swaged fitting. At a typical sailboat deck the rigging turnbuckle is located between the deck chain plate and the swage, and when the rigging is not under load the turnbuckle is free to rock back and forth in motion with the boat. This motion and the weight of the turnbuckle apply a bending load to the cables that exit the swage fitting and slightly bend them back and forth. Small bundled rods as in the patent application publication would not only bend but would also wear against each other at this exit location.)